As an irradiation method employed in a particle therapy device, there is known: a layer-stacking conformal irradiation method in which an irradiation target is virtually partitioned into a plurality of layers in order of depth from the body surface and irradiation is performed for every layer; and a scanning irradiation method. In employing either irradiation method, it is required to precisely recognize a dose during irradiation in order to perform irradiation in line with a target dose planned by a treatment plan device; however, it is impossible to place (implant) a dosimeter in a body as the irradiation target. As a result, generally, the dose (actual dose) in the irradiation target is estimated based on a measurement value of a dose monitor placed upstream of the body surface in the traveling direction of the particle beam.
However, since the particle beam is not a parallel beam, but a fan beam or cone beam having a spread, variations in dose due to positional differences in the body within a diseased site are not reflected in the measurement value by the dose monitor, so that it is difficult to convert the value simply into an actual dose.
In this respect, there is disclosed a particle therapy device that performs calibration using a dose calibration factor that has been measured for every irradiation condition for treatment in consideration of influences not only by an atmospheric temperature and an atmospheric pressure but also a mechanical characteristic, on a relationship between the actual dose and the measurement value by the dose monitor (for example, see, Patent Document 1). Furthermore, there is also disclosed a particle therapy device that calculates a dose calibration factor for every layer in a layer-stacking conformal irradiation method or a scanning irradiation method (for example, see, Patent Document 2).